Organic EL devices which utilize organic substances are expected to be useful for application as an inexpensive full color display device of the solid light emission type having a great size and various developments on the organic EL devices are. being conducted. In general an organic EL device has a construction comprising a light emitting layer and a pair of electrodes sandwiching the light emitting layer. The light emission of the organic EL device is a phenomenon in which, when an electric field is applied between the two electrodes, electrons are injected from the cathode side and holes are injected from the anode side, the electrons are recombined with the holes in the light emitting layer to form an excited state, and energy generated when the excited state returns to the ground state is emitted as light.
As compared with an inorganic light emitting diode, conventional organic EL devices require high driving voltage and only exhibited low luminance or low efficiency of light emission. Moreover, characteristic degradation of the conventional organic EL devices was also extravagant and as a result, they were not practically used. Although recent organic EL devices are improved step by steps, it has been still demanded to develop organic EL devices with an enhanced efficiency of light emission and with a prolonged lifetime.
For example, there is disclosed such a technique using a single monoanthracene compound as an organic light emitting material (refer to Patent Literature 1 below). However, in this technique, a luminance obtained by using the material is as low as 1650 cd/m2, for example, at a current density of 165 mA/cm2, and an efficiency of light emission thereof is very low, i.e., only 1 cd/A, which is practically unusable. Also, there is disclosed a technique using a single bisanthracene compound as an organic light emitting material (refer to Patent Literature 2 below). However, in this technique, a current efficiency of light emission obtained by using the material is also as low as around 1 to 3 cd/A. Therefore, further improvement of the technique has been demanded for rendering it practically usable. On the other hand, there is disclosed a technique using a distyryl compound adding styrylamine or so in an organic light emitting material in order for realizing an organic EL device with a prolonged lifetime refer to Patent Literature 3 below). However, the device described therein fails to show a sufficiently long lifetime and, therefore, further improvement has been demanded.
Furthermore, a technique of employing mono- or bis-anthracene compound and a distyryl compound as an organic light emitting medium layer is disclosed (refer to Patent Literature 4 below). However in these technologies, a conjugated structure of the styryl compound shifted a light emission spectrum in the long-wave direction and deteriorated the purity of color.
Still further, Patent Literature 5 below discloses a blue luminescence device with a of stilbene derivatives. However, despite the superiority in an efficiency of light emission, because the devices are not sufficient in its purity of color, further improvement for a purpose of full color displays application was required.
Patent Literature 1: Japanese Unexamined Patent Application                Laid-Open No. Hei 11-3782        
Patent Literature 2: Japanese Unexamined Patent Application                Laid-Open No. Hei 8-12600        
Patent Literature 3: International Application Published under                PCT No. WO 94/006157        
Patent Literature 4: Japanese Unexamined Patent Application                Laid-Open No. 2001-284050        
Patent Literature 5: International Application Published under                PCT No. WO 02/020459        